The art of finishing and reworking wells by restraining the passage of fluid from well holes into formation faces by means of compounds, cements or fillers forming filter masses is well known, as evidenced for example by J. B. Stone U.S. Pat. Nos. 2,353,372, Jul. 11, 1944 for Method of Preventing Fluid Loss from Well Holes into the Surrounding Earth; G. F. Williams U.S. Pat. No. 2,502,191, for Method of Preventing Loss of Liquid from a Well Hole in the Earth; and G. P. Maly U.S. Pat. No. 3,306,355, Feb. 28, 1967 for Formation Consolidation.
Thus, silicates, gravel, salt and calcium carbonate filled resin and like organic compound mixtures have been known in the prior art for sealing formation faces to prevent loss of fluids from a well casing. However a general and critical deficiency of these products is that once a sealing surface has been put into place, it is difficult to restore the sealed formation faces into a porous condition optimized for the output flow of liquids from the well after reworking. A similar problem in finishing a well is to produce a desired porosity for hydraulic stress purposes.
It is therefore an object of this invention to provide improved materials for plugging or matting geological formation faces and methods of restoring and controlling porosity in filter packs while processing wells.
Various prior art treatments for formation faces in the geological structure about the well casing with the objectives of controlling porosity for injection or withdrawal of fluids are known. For example there are methods for acid treatment of the geological structure to improve porosity. Thus, for example, organic material is removed from the siliceous geological formations by treatment with polyphosphoric acid with an objective of avoiding objectionable residues by D. C. Young, et al. in U.S. Pat. No. 4,101,425, Jul. 18, 1978 for Non-aqueous Acid Emulsion Composition and Method for Acid-treating Siliceous Geological Formations. The siliceous material in the geological structure is very slowly dissolved by low concentrations of acid to improve porosity by D. J. Blumer in U.S. Pat. No. 4,703,803, Nov. 3, 1987 for Composition and Method for Slowly Dissolving Siliceous Material and G. P. Maly, et al. in U.S. Pat. No. 4,101,426, Jul. 18, 1978 for Acid Composition and Method for Acid Treating Geological Formations. Also contaminants in gravel are treated with acids by J. T. Morine, U.S. Pat. No. 3,547,194, Dec. 15, 1970 for Method of Cleaning Gravel Packed, Gravel Developed and Drilled Igneous Wells.
None of these acid treatment methods however could be directed at treatment of the sealing surface produced on the formation faces after well reworking to establish an optimum permeability however, because the sealing surface materials are not generally acid soluble. Even in the use of impure packing grade calcium carbonate as a plugging material, acid solubility could not be controlled in a predictable manner to derive a controlled amount of surface porosity, and additionally leaves undesired contaminant residue.
It is accordingly an object of the present invention to provide acid soluble plugging and filtering materials for treating geological formation faces and methods of treating those sealing surfaces produced on the formation faces for control of permeability, such as by unplugging wells after the rework cycle to restore a desired production capacity through the geological formation face.
Other objects, features and advantages will be found throughout the following description and claims.